There are a significant number of viruses that can infect poultry. Such viruses include infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), Newcastle disease virus (NDV), Infectious Laryngotracheitis (ILTV), Mareks disease virus (MDV), Herpesvirus of Turkeys (HVT) which is also known as MDV3, and avian metapneumoviruses (aMPV). There also are a number of bacteria that can infect poultry, including Pasteurella multocida, Salmonella ssp., Escherichia coli, Mycoplasma ssp., Avibacterium paragallinararum, Erysipelas ssp., Campylobacter ssp., Vibrio ssp., and Clostridium perfringens. Parasites, such as Eimeria, also can infect poultry.
It is now widely accepted that the best way of preventing disease due to bacterial, parasital, or virus infections in poultry is to vaccinate them against these organisms. Moreover, multivalent live attenuated virus or bacterial vaccines can be safely administered that limit the number of vaccine injections required. Accordingly, there are many commercially available multivalent live virus vaccines that protect against multiple pathogens. However, heretofore, live attenuated avian viruses have been unstable when stored in liquid solutions. Therefore, most live attenuated avian virus vaccines are lyophilized, i.e., freeze-dried or frozen, prior to their long-term storage. The live attenuated avian virus is commonly mixed as a suspension in water with a protective agent, frozen, and then dehydrated by sublimation and secondary drying during the lyophilization process. The low temperatures of freezing and drying by sublimation, together with the low surface to volume ratios involved, can require long drying periods and thereby, significantly increase manufacturing time and costs.
In addition, there are inherent inconsistencies in large commercial drying processes due to: the inability to adjust the shelf temperature across the entire product load, variable freezing rates across the dryer, edge effects, and radiant energy effects. Increasing the drying temperature to reduce drying times is often not an option since the drying temperature has to remain significantly below the glass-transition temperature of the protective protein matrix. Moreover, the long inconsistent drying times and/or high drying temperatures often lead to structural damage to the live attenuated viruses, along with a significant loss of their biologic activity.
Consequently, in order to account for the inherent loss in efficacy, lyophilized poultry vaccines that comprise live attenuated viruses are stored with augmented titers. However, such increased titers can lead to significant adverse events should the lyophilization process actually lead to less loss of activity than anticipated. Therefore, great care is required to formulate a vaccine to contain a virus titer that is not only safely below the amount that leads to adverse events, but that also maintains sufficient efficacy in view of the virus titer loss due to lyophilization and subsequent storage.
Furthermore, there is a limitation to the size of a lyophilization vials and/or number of doses contained within such vials due to relatively small standard stopper sizes for the tops of these vials. Therefore, large volumes of liquid become difficult to sublimate through the relatively small openings. Therefore, there is a need for new live attenuated avian virus vaccines that can reliably retain their virus titers at a safe and efficacious level.
Additionally, the smallest vial size available for most poultry vaccines is 1000 doses. Vials of lyophilized vaccines must be used in their entirety after rehydration of the freeze dried cake. This makes it difficult for the growing number of small poultry farmers who have to buy a large dose size to vaccinate only a few birds. There is therefore a need for poultry vaccines where a single vial can be used over multiple days, weeks or even months, thus reducing the cost and encouraging vaccination of smaller flocks.
Finally, avian vaccines can be packaged with as many as 25,000 doses per vial, which are subsequently mixed by the user and placed in drinking water or sprayed on the flock. This requires the user to remove the metal sealing ring and stopper, flush the lyophilized vaccine out by submerging the vial in a large bucket of water, then mixing the solution with a large whisk or paddle. This is neither hygienic for the user or the poultry species for which the vaccine is intended. Indeed, dealing with lyophilized vials is particularly vexing in a commercial environment where the vaccine recipients, e.g., the fowl, reside.
The citation of any reference herein should not be construed as an admission that such reference is available as “prior art” to the instant application.